JSW08 Poster Nelson 202 37

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					                                                                                       Interdisciplinary studies of CDOM in the global ocean
                                                  Norman B.                                                       Nelson 1,                            Chantal M.                                    Swan 1,                         David A.                              Siegel 1,                          Craig A.                                           Carlson 1,2
                               1Institute               for Computational Earth System Science,                                                                                          2Dept.        Ecology, Evolution and Marine                                                    Biology, University                                              of California, Santa Barbara
Overview
                                                                                                                                                                                                                                          Global distribution and dynamics of CDOM in the surface and deep ocean
We are currently engaged in several research efforts concerned with the distribution, dynamics, and
characterization of chromophoric dissolved organic matter (CDOM) in the global ocean. These include:
                                                                                                                                                                                                                                          Norm Nelson, Dave Siegel, Craig Carlson
    •Ocean color algorithm development for retrieving CDOM absorption as well as chlorophyll and                                                                            EUCFe 2006                                                  Remote sensing of CDOM distributions in surface waters over the global                                                            CDOM Cycling Box Models
                                                                                                                                                                                                                        AMMA
    particulate backscatter in surface waters (with Stephane Maritorena). This has led us to new insight                                                                                                                2006
                                                                                                                                                                                                                                        ocean highlight a superficial correlation with chlorophyll and productivity, but
    concerning the influence of CDOM on retrieval of chlorophyll as well as pointing toward research on the                                                                                                                             with some significant differences. Significant CDOM in upwelling zones raised                            In these flow charts, the straight yellow arrows represent advective fluxes of CDOM (including
                                                                                                                                                                                             EqBOX                                      the question of whether CDOM was present in the ocean interior, if so what                               horizontal transport, upwelling, and downwelling), curled arrows represent local production of
    nature of CDOM cycling.                                                                                                                                                                  2005
                                                                                                                                                                                             2006                                       controlled its abundance in the deep sea, and how are the surface and interior                           CDOM, and the red arrows represent photobleaching. The top row of boxes represent surface
    •Time-series study of apparent and inherent optical properties at the BATS site southeast of Bermuda in                                                                                                                             coupled. We are in the process of conducting a global field survey of CDOM                               waters, and the second row represents the main thermocline down to 1 km. The color
    the subtropical North Atlantic. Our results have revealed a seasonal cycle in CDOM distribution that                                                                                                                                distribution and characteristics relative to hydrography, optics, and selected                           corresponds to CDOM absorption coefficient (as in the section plot to the left).
    indicated photolysis was the main sink, and secondary production the main source.                                                                                                                                                   biological parameters, as an ancillary project on the U.S. CO2/CLIVAR Repeat
                                                                                                                                                                                                                                        Hydrography surveys. Since 2003 we have collected data on meridional
                                                                                                                                                                                                                                        sections covering the full range of surface CDOM in every open ocean basin.
                                                                                                                                                                                                                                                                                                                                                                                 CDOM Dynamics: Atlantic
    •Photochemistry of CDOM: Measuring quantum yields for bleaching and photoproduction of CDOM on
    samples collected from the field in low CDOM areas where these rates are difficult to measure.                                                      Completed (full measurement set including CDOM, microbes, optics)
                                                                                                                                                                                                                                        Our results have highlighted the importance of thermohaline circulation and                                      North Atlantic           Subtropics                 EQ              Subtropics South Atlantic
                                                                                                                                                        Completed (limited measurement set, CDOM and hydrography)
Our results are leading to new insights concerning the nature and cycling of CDOM in the global ocean.                                                                                                                                  remineralization in determining the abundance of CDOM in the deep ocean. In
                                                                                                                                                        Future (in planning)
Ongoing and future efforts include characterization of CDOM along gradients of ventilation age, mixing, and                                                                                                                             the Atlantic, rapid meridional overturning mixes CDOM more homogenously,
photolysis using optical and chemical methods, and incorporation of CDOM terms into mixed layer and                                                                                                                                     rapidly transmitting surface CDOM concentrations to the interior. In the North
general circulation models.                                                                                                                        In surface waters, the distribution of CDOM is easily explained by a                 Pacific and Indian Ocean, slow mixing allows accumulation of CDOM formed
                                                                                                                                                   balance between production and photolysis. In subtropical waters                     as a result of remineralization. In the Southern Ocean, low production at the
                                                                                                                                                   persistent stratification and net downwelling leads to low CDOM                      surface and rapid ventilation transmit low CDOM signals to the interior,                                                                  Mode Water                                  Mode Water
                                                                                                                                                   concentrations. Formation of subtropical mode water in regions with                  creating the interhemispheric imbalance reflected in remotely sensed data.
Bermuda Bio-Optics Project: Decadal scale observations                                                                                             seasonal mixed layers carries low CDOM water to the ocean interior,
Norm Nelson, Dave Siegel                                                                                                                           where a low CDOM signature is easily observed in the mode waters of
                                                                                                                                                                                                                                                                                                                                                Arctic                                                                                                                        To
                                                                                                                                                   the North and South Atlantic. Meridional sections across the Equator                                                                                                                                                                                                                                                       ACC
                                                                                                                                                   clearly shows the transport of CDOM to the surface where it is
                                                                                                                                                   bleached.                                                                                                                                                                                                 Rapid meridional overturning allows little CDOM accumulation
  The contribution of CDOM to ocean
  color variability not related to                                                                                                                                                                                                                                                                                                                           Advection + bleaching balances net production
                                                                                                                                                   An outstanding question: is the high CDOM observed in the North
  chlorophyll abundance was first
                                                                                                                                                   Atlantic a residual of terrestrial CDOM from the Arctic? We hope to
  suggested by Siegel and coworkers
  studying the first year (1992) of in situ
                                                                                                                                                   resolve this with ongoing research and a repeat of the 2003 North                                                                                                                                              CDOM Dynamics: Pacific / Indian




                                                                                                                                                                                                                                                                                                                          acdom (325 nm, m-1)
                                                                                                                                                   Atlantic sections in 2011-2012.
  radiometry data from the Bermuda Bio-
  Optics Project, a time-series study of                                                                                                                                                                                                                                                                                                                 North Pacific            Subtropics                 EQ          Subtropics Southern O.
  optical properties in the water column
  piggybacking on the successful




                                                                                                                                                                                                                               acdom (443 nm, m-1)
  Bermuda Atlantic Time-series Study
  cruises.

  Since 1994 the real contribution of                                                                                                                                                                                                                                                                                                                                                                                         Mode Water
  CDOM to ocean color has been
  assessed using spectrophotometric                                                                                                                                                                                                                                                                                                                                                                                                                                           From
  measurements of CDOM absorption                                                                                                                                                                                                                                                                                                                                                                                                                                             ACC
  spectra, as part of an integrated study
  of component absorption.

  Sustained observations of CDOM are                                                                                                                                                                                                                                                                                                                         North: Long residence time allows CDOM accumulation
  being considered in the context of                                                                                                                                                                                                                                                                                                                         South: Production limited (iron?) Low surface signal carried
  climate-related changes in the factors
  controlling CDOM abundance.                                                                                                                           (Global CDOM map from SeaWiFS/GSM, mission mean)                                                                                                                                                     to depth by advection / water mass formation




                                                        At BATS, seasonal mixing homogenizes the CDOM                                              Quantum yield () of CDOM photolysis -- the major sink of CDOM                                                                                                        Photobleaching / photoproduction quantum yields
                                                        profile from a characteristic summer pattern that                                          Chantal Swan, NASA Earth System Science Fellowship
                                                        includes a surface minimum, a local maximum in the                                                                                                                                                                                      Sample Site   Latitude   Region                          Depth   T (°C)   Sal.      Chl-a    Initial aCDOM   Initial aCDOM    (325nm,325nm)   (440nm,440nm)   Total
                                                                                                                                                                                                                                                                                                                                                         (m)              (ppt)     (ug/l)   (m-1) at         (m-1) at        (m2 mol          (m2 mol          irradiation
                                                        60-150m range, and a local minimum in the mode                                              • Photolysis moderates global surface distribution of CDOM                                                                                                                                                                                                                photons-1)       photons-1)
                                                                                                                                                                                                                                                                                                                                                                                             325nm           440nm                                              time (days)
                                                        water. But this mean pattern summarizes much
                                                        variability. We are examining interannual patterns in                                                                                                                                                                                   PB189S5       34°N       Coastal Pacific                 0       16       33.1      0.600    0.20            0.02             -0.08            -0.004           2.02
                                                        CDOM distribution in the upper water column to assess                                       •  (and photolysis rate) can be used in concert with upper ocean vertical mixing rate to deduce                                                                     (So. Cal. Bight)

                                                        the relative contribution of local effects (production,                                     microbial production rate of CDOM (a term otherwise hard to measure)                                                                        BATS          32°N       Subtropical
                                                                                                                                                                                                                                                                                                                         N. Atlantic
                                                                                                                                                                                                                                                                                                                                                         80      23       36.6      0.200    0.06            0.001            -0.05            -0.001           3.02

                                                        mixing) versus remote effects (mode water formation,                                                                                                                                                                                    P16NS51       29°N       Subtropical                     140     19       35.2      0.078    0.07            0.003            -0.09            -0.002           2.97
                                                        overall irradiance leading to photolysis). An intriguing                                    • Constraining a mixed-layer budget of CDOM will permit its use as the first remotely-sensed tracer of                                                               N. Pacific
                                                        hint of CDOM-climate teleconnections can be seen in a                                                                                                                                                                                   P16NS51       29°N       Subtropical                     40      20       35.3      0.096    0.05            0.001            -0.05            0                3.06
                                                        correlation between the North Atlantic Oscillation and
                                                                                                                                                    upper ocean circulation                                                                                                                                              N. Pacific

                                                        CDOM abundance at 160 m.                                                                                                                                                                                                                P16NS76       55°N       Subarctic                       200     4        33.9      0.004    0.17            0.02             -0.07            0.004            2.00
                                                                                                                                                    Key Findings:                                                                                                                               P16NS76       55°N
                                                                                                                                                                                                                                                                                                                         Pacific
                                                                                                                                                                                                                                                                                                                         Subarctic                       80      3        33.0      0.019    0.14            0.01             -0.03            0.009            2.00
                                                                                                                                                                                                                                                                                                                         Pacific

Acknowledgments:                                         Publications 2007-08                                                                      • Loss of CDOM absorption in the UV due to full-spectrum solar irradiation occurs in nearly all regions                                      P16NS19       0.5°N      Equatorial                      100     22       35.6      0.060    0.06            0.005            -0.05            0.015            2.95
                                                                                                                                                                                                                                                                                                                         Pacific
NASA Ocean Biology and Biogeochemistry                   Goldberg, S.J., D.A. Hansell, N.B. Nelson, D.A. Siegel, and C.A. Carlson, (submitted to   sampled. We can constrain environmental range of open ocean photolysis                                                                      P16SS61       46°S       Subantarctic Pac.               80      10       34.4      0.242    0.07            0.01             0                0.012            2.06
NSF Chemical Oceanography                                Deep-Sea Research I). Temporal dynamics of dissolved combined neutral sugars and the                                                                                                                                                                            Frontal Zone
U.S. CLIVAR/CO2 Repeat Hydrography Project               quality of dissolved organic matter in the northwestern Sargasso Sea.                                                                                                                                                                  P16SS61       46°S       Subantarctic Pac.               0       13       34.4      0.132    0.05            0.01             0                0.008            3.01
(Jim Swift, Lynne Talley, Dick Feely, Rik Wanninkhof,    Nelson, N. B., D. A. Siegel, C. A. Carlson, C. Swan, W. M. Smethie, S. Khatiwala
                                                                                                                                                   • 50% of regions sampled show a very unexpected concurrent phenomenon at longer wavebands:                                                                            Frontal Zone
Rana Fine)                                               (2007). Hydrography of chromophoric dissolved organic matter in the North Atlantic.       formation of CDOM due to irradiation
UCSB Field Teams: Dave Menzies, Jon Klamberg,            DeepĞ Sea Research I. doi:10.1016/j.dsr.2007.02.006                                                                                                                                                                                   Table: Summary of associated hydrographic data and calculated  values (325nm and 440nm, shaded blue). Sites and values marked in red
Meredith Meyers, Ellie Wallner, Meg Murphy, Natasha                                                                                                                                                                                                                                            denote where (440nm;440nm) is positive, corresponding to observed photoproduction of CDOM during irradiation.
                                                         Swan, C. M., N. B. Ne lson, D. A. Siegel, C. A. Carlson, E. Nasir (to be submitted to
McDonald                                                 Deep-sea Research I). Biogeochemistry of chromophoric dissolved organic matter in the      Schematic of inversion terms using Subtropical N. Atlantic (BATS) example:
Hansell Group: Dennis Hansell, Charlie Farmer,           Pacific.
Wenhao Chen                                                                                                                                                       daCDOM/dt (measured)                        E0*ācdom                                    E0*ācdom*(o=325nm)                 • (o=325nm) has distinct range over all irradiation
Bill Landing (FSU) and Chris Measures (UHI) (Water       Presentations2007-08                                                                                                                                                                                                                  wavelengths in regions sampled
samples)                                                                                                                                                                                                         Time
                                                         Nelson, N. B., D. A. Siegel, C. A. Carlson, C. M. Swan, S. J. Goldberg (2008). Invited
Bill Smethie & Samar Khatiwala, LDEO (CFC ages)
                                                         Talk, ASLO Ocean Sciences, Orlando, FL: CDOM in the deep sea: distribution and
                                                                                                                                                         Time
                                                                                                                                                                                                                                                                                               • What are the controls on ?
Ru Morrison & Mike Lesser, UNH (MAA analysis)            dynamics from trans-ocean sections.
Wilf Gardner and Team, TAMU (C-Star
                                                         Swan, C. M., D. A. Siegel, N. B. Nelson, T. S. Kostadinov (2008). Poster, ASLO Ocean                                                                                                                                                  Initial aCDOM explains roughly half of the variance in 
transmissometer)
Mike Behrenfeld and Team, OSU (Equatorial BOX
                                                         Sciences, Orlando, FL: Photochemical cycling of chromophoric dissolved organic matter                                                                                                                                                 (r2=0.56, n=18)
                                                         (CDOM) in the open sea: Comparison of photolytic quantum yields among ocean
project)                                                 regions. (See attached 08_ASLO_poster_S  wan.pdf)
Erica Key and Team, U Miami (AMMA-RB 2006)                                                                                                                                                                                                                                                     In situ temperature does not explain any variance in 
                                                         Swan, C. M., N. B. Ne lson, D. Siegel, C. A. Carlson (2007). Talk, ASLO Aquatic                                                                                                                   Time
Jim Murray and Team, UW (EUCFe 2006)                     Sciences, Santa Fe, NM: Hydrography of chromophoric dissolved organic matter
                                                                                                                                                                                                                                                                                               (r2=0.02, n=18)
R/Vs Brown, Knorr, Revelle, Melville, Thompson, Ka’I,    (CDOM) in the Pacific Ocean.
Kilo Moana

				
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